1. Field of the Invention
The invention relates to storage tanks generally, and more particularly to a retainer system for securing a tank to an anchor such as a deadman or a slab.
2. Discussion of the Background
Underground storage tanks are commonly used for the storage of liquids, including gasoline, other petroleum products, and wastewater. These tanks are generally cylindrical in shape, with either curved (e.g. hemispherical) or flat ends. Underground storage tanks may be made of many materials, including steel and fiber reinforced plastic (referred to herein as FRP and fiberglass). Such tanks may be single or multi-walled.
USTs are installed in a wide variety of locations and under a wide variety of conditions. In some locations, the water table is high enough such that some or all of the UST is below the water table. In these situations, a buoyant upward force will act on the tank. If the buoyant force exceeds the downward forces acting on the tank, the tank will ‘float’ up out of the ground (referred to herein as flotation). This situation is obviously undesirable.
One method commonly used to ensure that flotation does not occur is through the use of anchors such as slabs or deadmen. Slabs and deadmen are typically constructed of reinforced concrete. A slab is typically several inches thick and wider and longer than the corresponding tank. A deadman is typically 12 to 36 inches wide, 8 to 12 inches high, and usually has a length equal to or greater than the corresponding tank. Deadmen are typically installed on both sides of a tank. A detailed discussion of slabs and deadmen, and their use in anchoring underground storage tanks can be found in co-pending U.S. application Ser. No. 09/657,807, filed on Sep. 8, 2000, entitled “Underground Storage Tank Buoyancy and Buoyancy Safety Factor Calculation Method and Apparatus,” which is commonly owned by the assignee of the present application and which is hereby incorporated by reference herein.
Tanks are commonly attached to anchors such as slabs and deadmen using straps. The straps are commonly used in pairs, with each strap connected on one end to a hook that is engaged with a loop, or lug, on the anchor. In one embodiment, the other ends of the straps are connected to each other.
In the past, tightening mechanisms, such as turnbuckles, were typically located at both ends of the straps near the anchor lugs. This tightening mechanism could not be operated if located at a position where it was in contact with the tank. This arrangement requires installation personnel to enter the excavation pit in which the tanks were located in order to install and tighten the straps. This practice was potentially unsafe because it is possible for excavation sidewalls to collapse unless very expensive shoring was used. Additionally, if there was water in the hole, tightening was difficult.
The aforementioned problems with traditional strap systems led Xerxes Corporation (“Xerxes”) to develop the “Man Out of the Hole” system approximately 15 years ago. In this system, a tightening mechanism was developed that could be located on top of the tank so that it could be operated by an installer standing on top of the tank, thereby doing away with the need for installation personnel to enter the excavation pit during installation. This system proved effective and has since been adopted by a large portion of the industry.
While the original Man Out of the Hole system has been a dramatic improvement and has generally proven effective, it is not optimal. First, the system requires installation personnel to maneuver the hook end of the strap onto the retaining loop on the anchoring system, and to maintain tension on the strap once hooked to avoid having the hook disengage from the anchor retaining loop. This operation requires patience, and time, especially on the part of inexperienced installation personnel. Second, the Man Out of the Hole system uses a threaded rod positioned above the tank so that the middle of the rod clears the tank. The rod is supported by a pair of brackets, each of which is attached to a strap. A bending force may be created by this elevated rod which means that the brackets need to be strengthened to support this force.
What is needed is an improved system that in which the strap hooks are more easily engaged with the retaining loops and a less expensive tightening mechanism that places less bending force on the brackets, is simple, and cost effective.